Soil erosion hazard prediction by SWAT model and fuzzy logic in a … · 2011. 6. 23. ·...

Soil erosion hazard prediction by SWAT model and

fuzzy logic in a highly mountainous watershed

Isfahan University of Technology

Introduction

Challenges

Soil erosion

A major environmental threat to the sustainability and productive

capacity of agriculture (Bakker et al., 2004; Metternicht and Gonzalez,

2005; Yang et al., 2009).

Reduction of soil fertility and loss of nutrients and thus, declines of

crop yields in farmlands (Yang et al., 2009).

Degradation of the quality of surface and ground water (Mitra et al.,

1998; Kim and Gilley, 2008).

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Introduction

Challenges

Iran is one of the worst affected countries by land degradation

and soil erosion in Asia (FAO, 1991).

Mean annual soil erosion rate in Iran: about 25 tons/ha/year,

4.3 times more than the mean annual soil erosion rate in the

world (Ahmadi Ilkhchi, 2003; Rostamian et al., 2008).

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Introduction

Challenges

Many parts of Iran are subjected to a high and

very high soil erosion hazard

Introduction

Challenges

A few areas of a large watershed might be critical and more

responsible for high amount of soil and nutrient losses (Tripathi et al.,

2003)

Implementation of the best management practices in those critical

erosion prone areas

Identification of these critical areas is essential for the effective and

efficient implementation of watershed management programs.

Introduction

Challenges

Using physically based distributed parameter models, RS, and

GIS techniques may assist management agencies for identifying

the most vulnerable erosion-prone areas of watersheds and

selecting appropriate management practices.

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Objectives

Identification and prioritization of critical sub-basins in a

highly mountainous watershed

Main Objective

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Objectives

Estimation of runoff and sediment load in a highly mountainous

watershed with imprecise and uncertain data using soil and water

assessment tool (SWAT) model

Developing a GIS-based fuzzy logic map for predicting soil erosion

hazard in a very large watershed

Study area

Bazoft Watershed

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One of the main sub-basins in Iran where the land degradation and

soil erosion have contributed to major economical, social, and

environmental problems

Study area description

Bazoft watershed

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The major slope class: 40-70%

(covers an area of about 46 %).

Highly mountainous

Study area description

Bazoft watershed

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Pastures

Forests

Agricultural and bare lands

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The impact of human and livestock population is exacerbated the rapid depletion of the natural resource bases in the watershed.

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Conversion of wood and rangelands into croplands: Severe soil erosion in many parts of the watershed

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Different Types of Soil Erosion

An urgent need to perform an comprehensive study to assess the

future risk of soil erosion in this watershed for an appropriate

conservation and sustainable rehabilitation of the land

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Different parts of the study: Soil Erosion Hazard Prediction Using:

SAWT Model

Fuzzy Logic Algorithm

Soil Erosion Hazard Prediction using

SWAT model

Part 1

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Part 1 SWAT model

Continuous time, spatially semi-distributed model, developed to

simulate the impact of management decisions on water, sediment and

agricultural chemical yields in river basins in relation to soil, land use

and management practices (Arnold et al.,1998).

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Hydrometric stations are quite limited in the Bazoft

watershed.

Management plans are difficult to develop due to

the lack of measured data.

Imprecise and uncertain data

Part 1 SWAT model

Problems:

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The SWAT model has been used globally as well as in Iran to

assess water quality, runoff and sediment load, and soil erosion

predictions.

A useful tool for runoff and sediment simulation in watersheds

with imprecise and uncertain data

Part 1 SWAT model

Materials and Methods

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Part 1 SWAT model

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The basic input data to the SWAT:

digital elevation model (DEM) stream network land-use soil climate data

Part 1 SWAT model

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DEM

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Grid size of 53m × 53m

Part 1 SWAT model

Land Use Soil Map

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41 Sub-basins 406 HRUs

Part 1 SWAT model

By entrance of different maps into the

model, the watershed was subdivided into:

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Climate Data

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Climate data including daily precipitation, max

and min air temp, were obtained from existed

climatic and meteorological stations from different

organizations.

Part 1 SWAT model

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Simulation time period: 1989 - 2008

Part 1 SWAT model

Calibration and Validation

Runoff Sediment

Calibration: 1995-2008 Validation: 1989-1994

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Calibration and Validation

SWAT-CUP

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Part 1 SWAT model

Model calibration and uncertainty analysis: SUFI-2, the programs interfaced with SWAT, in the package SWAT-CUP

SWAT-CUP

Results and Discussion

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Part 1 SWAT model

Sensitivity Analysis

An initial sensitivity analysis were performed for choosing the sensitive parameters

Part 1 SWAT model

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Runoff r_CN2.mgt

r_SOL_BD.sol

r_SOL_AWC.sol

r_SOL_K.sol

r_SOL_ALB.sol

v_ALPHA_BF.gw

v_GW_DELAY.gw

v_REVAPMN.gw

v_GW_REVAP.gw

v_SHALLST.gw

v_RCHRG_DP.gw

v_GWQMN.gw

v_EPCO.hru

v_ESCO.hru

v_SLSUBBSN.hru

v_OV_N.hru

v_CH_N2.rte

v_CH_K2.rte

v_SFTMP.bsn

v_SMTMP.bsn

v_SMFMX.bsn

v_SMFMN.bsn

v_TIMP.bsn

v_MSK_CO1.bsn

v_MSK_CO2.bsn

v_SURLAG.bsn

Sediment v_ADJ_PKR.bsn

r_USLE_K.sol

v_SPCON.bsn

v_SPEXP.bsn

v_CH_EROD.rte

v_CH_COV.rte

v_USLE_P.mgt

v_LAT_SED.hru

v_HRU_SLP.hru

v_FILTERW.mgt

Sensitivity Analysis

Part 1 SWAT model

Calibration Runoff

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p-Factor = 0.64

r-Factor = 1.10

n-s=0.62

Part 1 SWAT model

Validation Runoff

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Part 1 SWAT model

p-Factor = 0.62

r-Factor = 0.91

n-s= 0.55

Calibration Sediment

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p-Factor = 0.71

r-Factor = 1.03

n-s= 0.54

Part 1 SWAT model

Validation Sediment

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Part 1 SWAT model

p-Factor = 0.59

r-Factor = 0.91

n-s= 0.48

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Identification and prioritization of critical sub-basins

in the Bazoft watershed

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Part 1 SWAT model

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19 out of 41 sub-basins fell into the

high and very high soil erosion

categories, of which 17 sub-basins were

in the very high category

Part 1 SWAT model

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After arranging the sub-basins in

ascending order, sub-basins S5, S6, S4,

and S31 were accounted for about 76%

of the total soil loss from the

watershed while they cover only about

11% of the total area of the

watershed,.

Part 1 SWAT model

Soil Erosion Hazard Prediction using

Fuzzy logic algorithm

Part 2

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Fuzzy systems (fuzzy sets, membership functions, and fuzzy

production rules) provide a rich and meaningful improvement

extension of conventional logic, introduced by Zadeh (1965).

A generalization of classic (Boolean) set theory (McBratney and

Odeh, 1997).

In traditional set theory, an element either belongs to a set, or it does not

(0 or 1, black or white…).

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Part 2 Fuzzy logic algorithm

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Example: Height

Tall people: say taller than or equal to 1.8m

1.8m , 1.9m, 2m etc member of this set

1.5 m, 1.6 m or even 1.79999m not a member


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Example: Height

By the help of Fuzzy logic: you are now a member of this set

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Membership functions classify elements in

the range [0,1], with 0 and 1 being no and

full inclusion, the other values being partial

membership

Membership functions

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Fuzzy production rules represent human knowledge in the form of ‘IF-THEN’ logical statements.

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IF temperature IS very cold THEN stop fan.

IF temperature IS cold THEN turn down fan.

IF temperature IS comfortable THEN maintain fan speed.

IF temperature IS hot THEN speed up fan.

Fuzzy rules


Materials and Methods

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Vegetation cover

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Slope Soil erodibility

Three main landscape elements related to soil erosion in the study area

for predicting soil erosion hazard using fuzzy logic approach:

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The algorithm for fuzzy logic model development provided in :


Results and Discussion

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A large part of the watershed was predicted to be endangered from a high or very high erosion risk


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Identification and prioritization of critical

sub-basins in the watershed

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27 out of 41 sub-basins fell into

the high and very high classes

(accounted for about 74% of total soil

loss from the watershed)


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Sub-basins S30, S28, S33, and S6

were more critical and assigned as

the top priorities for developing

appropriate management practices.


Evaluating the obtained results for identifying and

prioritizating of critical sub-basins in the watershed

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Field Surveys

Interpretation of satellite photos

Governmental and non-governmental reports

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S6

S4

S31

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Iran

The SWAT model is recommended for identifying and prioritizing

the critical sub-basins for management purposes in the Karun

catchment.

For the future

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A large part of the watershed was predicted to be endangered of a

high or very high erosion risk.

The SWAT model may be more reliable in identifying and prioritizing

the critical sub-basins for management purposes in the study area than

the Fuzzy logic model.

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Conclusions

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Limited data available in the study area: the method

developed herein may help us to find more critical sub-basins

The method can be applied in other watersheds

Many developing countries: measured data are unavailable in each

sub-basin of a watershed.

Conclusions

Khaju Bridge, Isfahan, Iran

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The simulation time period: 1989 - 2008

Part 1 SWAT model

Karun 4 dam at the outlet of the watershed

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